Due to the high hardness, extremely low electrical conductivity, low frictional coefficient, and low chemical affinity of diamond-like carbon (DLC) films, they have been widely used in the applications in which low wear and anti-corrosion are required, such as semiconductor industry and wear resistant mechanical components.
The microstructure of DLC films is non-crystalline, in which both sp.sup.2 and sp.sup.3 bondings exist. The DLC films can be categorized into two types: one is hydrogenated DLC film and the other is non-hydrogenated DLC film.
The hydrogenated DLC film is usually obtained by means of cracking of hydrocarbon gases, such as plasma enhanced chemical vapor deposition (PECVD), hot filament chemical vapor deposition (HFCVD), or laser ablation. The non-hydrogenated DLC film is obtained by, for instance, magnetron sputtering, electron beam evaporation, or cathodic arc evaporation (CAE). It is noted that CAE can achieve high ionization and control the kinetic energy of ions to realize a DLC film having high hardness.
The primary disadvantages of the DLC films made by the above methods are the high internal stress and poor adhesion and thus the deposit thickness is as low as 0.2 to 1.0 micron, thereby resulting in ineffective application in mechanical dies or components.
In order to overcome the problem, several methods have been proposed. Franceschini, et al. (Applied Physics Letters, vd 60, No. 26, (1992) 3229-3231) incorporated nitrogen into hydrogenated DLC films to relief the internal stress and this improved to some extent. Falabella, et al. (U.S. Pat. No. 5,474,816, Dec. 1995) proposed a method for depositing DLC films by CAE with a graphite target, wherein, as disclosed in the patent, a metal was incorporated as an interlayer or nitrogen was added to the DLC films in order to reduce the internal stress. However, two or more target materials have to be provided in the same evaporation system according to this method. D. P. Monagham, et al. (Surf and Coat Technology, 60 (1993) 525-530) proposed a process of PECVD combined with magnetron sputtering to produce a DLC film comprising a metal interlayer and impurities, the advantage of which is a low temperature combination of PVD and PECVD for the DLC production. However, for the sake of its limited ionization energy of asymmetrical magnetron sputtering system, the hardness of the film thus obtained is between that of metal nitrides and that of conventional DLC, and the deposition rate is also low.
The other related prior arts are, for example, disclosed in the patents U.S. Pat. No. 5,401,543 issued to O'Neill, et al. (March 1995), U.S. Pat. No. 5,653,812 issued to Salter Richy Leonard, et al. (August 1997), U.S. Pat. Nos. 5,725,573 and 5,731,095 issued to Lankford Jr. James, et al. (March 1998), U.S. Pat. No. 5,799,549 issued to Decker, et al. (September 1998), U.S. Pat. No. 5,763,087 issued to Falabella, et al. (June 1998), and W.O. 9810115 issued to Brown David, et al. (March 1998), as well as those described by S. Prawer, K. W. Nugent, et al. (Diamond and Related Materials, 5 (1996) 433-438) and D. G. McCulloch, S. Prawer, et al. (Physics Review B, 50 (1994) 5907-5917). They are also incorporated herein by reference.
The foregoing patents and documents reflect the state of the art of which the applicant is aware and is tendered with the view toward discharging the applicant's acknowledged duty of candor in disclosing information that may be pertinent in the examination of this application. It is respectfully stipulated, however, that these patents do not teach or render obvious, singly or when considered in combination, the applicant's claimed invention.